Protein kinase C dependent and independent mechanisms controlling rat trophoblast cell DNA synthesis and differentiation.

Trophoblast giant cells are the steroidogenic cells of the rat placenta. In this study, the role of protein kinase C signalling pathways in the control of DNA synthesis and differentiation-dependent progesterone biosynthesis by trophoblast cells were investigated. Rcho-1 trophoblast cells, derived from a rat choriocarcinoma, can be experimentally manipulated to proliferate or differentiate and provide a useful model for studying trophoblast giant cell endocrine differentiation. The role of protein kinase C signal transduction was examined through the treatment of Rcho-1 trophoblast cells with isoquinolinesulfonamide derivatives (H7, a protein kinase C inhibitor; HA1004, a control compound), chelytherine (a protein kinase C inhibitor), and phorbol esters (protein kinase C activators). Treatment with H7 significantly attenuated DNA synthesis in proliferating and differentiating trophoblast cells and accelerated the acquisition of progesterone biosynthetic capabilities by trophoblast cells. Treatment with HA1004, the related but functionally distinct isoquinolone, did not significantly affect trophoblast DNA synthesis or proliferation and only weakly increased progesterone accumulation. Chelytherine significantly inhibited trophoblast cell proliferation but failed to influence trophoblast progesterone production significantly. The phorbol ester, 12-O-tetradecanoylphorbol acetate, did not significantly influence progesterone accumulation. H7 did not significantly influence the concentration of either P450scc or the mRNA encoding it in Rcho-1 trophoblast cells, or the transcriptional activity of the P450scc gene. The results indicate that signalling pathways sensitive to protein kinase C are involved in the control of trophoblast cell proliferation. Differentiation-dependent production of progesterone is sensitive to H7 but appears to be independent of protein kinase C and occurs at a stage other than P450scc expression.